Coronary artery bypass grafting (CABG) is the most common procedure performed by cardiac surgeons. Post-operative atrial fibrillation (AF) is the most common adverse event following CABG, experienced in 20-50% of patients; the highest incidence of AF occurs by the third post-operative day. Reduction of AF by various drugs is moderately effective, but involves either rate control with beta blockers or rate conversion with amiodarone after the myocardial damage processes initiating AF have already occurred. Decreasing the incidence of post-operative AF, and hence the morbidity and mortality of high-risk CABG patients, could be more fruitfully approached by targeting the upstream combined processes of inflammation and coagulation activation induced by the surgical insult and associated ischemia-reperfusion (I/R). We propose that cell damage induced by oxidative stress and I/R injury could be prevented and/or inhibited by antioxidant supplementation. Specifically the investigators hypothesize that high-dose intravenous (IV) vitamin C supplementation will ameliorate ROS and therefore damp down upstream inflammatory processes, leading to a reduction of downstream adverse events with demonstrable links to inflammation processes, such as AF.